1. Field of the Invention
This application relates to a mold closing unit for use in an injection molding machine comprising a stationary mold carrier, a movable mold carrier constituting a mold clamping space together with the stationary mold carrier between the movable mold carrier and the stationary mold carrier, a mold comprising at least two parts mounted on the stationary mold carrier and the movable mold carrier, a first device adapted to transfer the movable mold carrier into and out of a closing position with the stationary mold carrier for closing the parts of the mold within the mold clamping space, a first supporting element for supporting at least the first device connected with the stationary mold carrier by force transmitting means, a second device for generating a closing force engagable after the first device during mold closure of the mold and acting on the first device, the first supporting element and the movable mold carrier.
This application relates furthermore to a process for controlling such a mold closing unit with at least one first force sensing means for sensing an actual force occurring in moving the movable mold carrier and in generating the closing force and adapted to sense the actual force only at a time before the second device is actuated, the process comprising the steps of:
setting of a first maximum force limiting the actual force occurring in moving the movable mold carrier from a start position into the closing position, PA1 setting of a touch force to be generated by the first device when the at least two parts of the molds are in the closing position, PA1 sensing the actual force occurring in moving the movable mold carrier and in generating the closing force via the first force sensing means, PA1 comparing the actual force with the first maximum force and stopping the moving of the movable mold carrier when the actual force is higher than the first maximum force. PA1 setting of a touch force to be generated by the first device when the at least two parts of the molds are in the closing position, PA1 setting of a maximum closing force, PA1 calculating a partial force to be generated by the eccentric drive in subtracting the touch force from the maximum closing force, PA1 setting of a control area, wherein the eccentric drive is controllable within the control area to maintain the closing force; the control area is terminated by a dead stop, where the eccentric drive is at least nearly stretched, PA1 calculating a way of deformation arising in generating the partial force by the eccentric drive after the touch force was generated by the first device and adding a way corresponding to the control area, PA1 calculating a remainder angle necessary for generating the way of deformation and the way corresponding to the control area when turning the eccentric drive into the dead stop, PA1 calculating a supplementary angle amending the remainder angle to 180 degree, PA1 driving the eccentric drive to set the supplementary angle measured from a zero position, wherein the eccentric drive has a smallest length, PA1 carrying out at least one cycle comprising the steps:
This application relates also to a process for controlling such a mold closing unit wherein the second device for generating the closing force is an eccentric drive, a shaft of which is adapted to generate the closing force on the first device, and comprising at least one second force sensing means for sensing an actual force occurring in moving the movable mold carrier and in generating the closing force, wherein the process comprises the steps of:
closing the at least two parts of the mold and generating the touch force via the first device, PA2 generating the closing force via the eccentric drive in turning the eccentric shaft to generate the partial force, PA2 injecting of the plastifiable materials to produce a molding, PA2 sensing the actual force via the second force sensing means and comparing the actual force with the maximum closing force to establish a set value for the eccentric drive, PA2 controlling the eccentric drive within the control area via the set value at least during injection, PA2 turning back the eccentric drive around the remainder angle, PA2 removing the touch force and opening the mold via the first device to remove the molding from the mold.
2. Description of the Prior Art
A mold closing unit of this kind is known from JP-A 62-64520. In this device the movements arising during the mold closure are assigned to different subassemblies. A first subassembly is a toggle mechanism driven via a ball screw. The main function of the toggle mechanism is to transfer the movable mold carrier into and out of a closing position with the stationary mold carrier. After approaching the two parts of a mold, however, there still remains a split. The rest of the movement is effected by a second device engaging at a screw bushing, which at the same time is the bearing of the ball screw. The first step of the movement, that is, until the mold is closed, is effected by this mechanism by applying high speed and a low moment of torsion. For the purpose of concluding the mold closure definitely the second device has to be used. Thereupon the second device switches over to an operating method with a high moment of torsion, so that the closing force can be brought up by the second device and interconnection of the first device. Since the individual tasks are not assigned clearly to the two devices, costly gearings and change-over steps are necessary, even if a supporting element for the first device is movably supported, so that the whole unit can be supported at the supporting element for the second device.
In a mold closing unit according to International Published Application WO 92/11993 the movements necessary for the mold closure in an injection molding machine are distributed on two subassemblies, which are actuable consecutively in two steps. A spindle drive is used for displacing the movable mold carrier, whereas a hydraulic cylinder is provided for generating the closing force. The threaded spindle is movably supported in the plunger piston of the hydraulic cylinder. Both elements are supported at a common supporting element. When the threaded spindle is actuated, it is maintained in a zero-position by spring means, so that a resilient suspension of the threaded spindle is created, which might cause difficulties when the closing force is brought up. During the generating of the closing force the threaded spindle--in case it is not irreversible--has to be kept in contact by its drive motor to avoid a reversed rotation. At the same time the threaded spindle serves as closing force transmitter and closing force generator.
A further mold closing unit of this kind is disclosed in European Patent 271 588. In this unit two spindle systems are connected in series. The spindle systems are actuated consecutively, wherein couplings are provided adapted to isolate the respective not used spindle from the power flux. The double expenditure of the spindle bearing with respect to the full closing force should not be underestimated. For fixing the spindle it is also possible to provide braking means or claw couplings, which spring is adjusted in a way that a reaction force realizes the coupling during the mold closure.
In Published German Patent Application P 43 45 034 and the counterpart International Published Patent Application WO 94/22655 a process for the control of an electrical driven injection molding machine is described. To realize a reliable control of the forces occurring in moving the movable mold carrier, the sole use of a toggle lever mechanism for mold closure is suggested. The toggle lever mechanism is driven via a servo motor and the force is determined during the closing cycle, for example; in sensing the current of the motor necessary for moving the movable mold carrier or at the joint of the toggle lever. The hereby determined value is compared with a desired curve and watched. However, because only one drive generates the complete mold closure, the force sensor must be able to sense all the forces occurring at the machine from zero to the maximum closing force. A sensitive control of the closing movement is therefore not possible. A control of the generated mold closing force, after the mold is closed is neither intended nor possible. However, such a control can only be realized with a large amount of energy, because the toggle lever mechanism can only work economical in its most stretched position.